This invention relates generally to improvements in methods and apparatus for effecting an electrotherapeutic treatment on a biological subject, such as iontophoretic delivery of medicaments and, more particularly, to a new and improved system for the application of an iontophoretic treatment topically to the skin of a human body.
Around the turn of the century there was disclosed a plethora of electrode types for applying xe2x80x9celectric treatmentsxe2x80x9d to the human body. The electrodes were normally placed upon the body in relation to the position of the organ to be treated. Such xe2x80x9celectric treatmentsxe2x80x9d encompassed a wide range of applications. For example, galvanic (direct current) treatments have been popular in the past for their polar effects on ionized molecules, causing the ionized molecules to be driven through the skin, usually superficially. This phenomenon is known as iontophoresis or ion transfer, and it has been employed for the introduction of medicaments or even simply moisture, into the skin of a patient.
More specifically, and by way of example, some ions of zinc and copper can be employed in the treatment of various skin infections, and chlorine ions have been employed for the loosening of superficial scars. Further, vasodilating drugs can be used in rheumatic and peripheral vascular affections, and skin anesthesia can be produced by iontophoresis of local anesthetic drugs. Moreover, iontophoretic administration of drugs typically avoids the gastrointestinal side effects sometimes associated with direct ingestion of such drugs.
Although the aforementioned iontophoretic treatments have been found to be effective, they are also known to be accompanied by a number of undesirable side effects, such as the occurrence of skin injury in the form of iontophoretic burns and irritation in the treated area, as well as the formation of undesirable vesicles and bulla, on the skin in the treated area. Various complicated or compromised methods for preventing these iontophoretic burns have been developed. However, such methods and apparatus have generally been found not to be adequately effective for preventing irritation and the formation of vesicles or bulla on the skin in the treated area. Consequently, iontophoretic treatments have usually been limited to relatively low electrical currents and relatively short periods of administration of, typically, twenty, minutes or less.
Iontophoretic drug delivery systems of the prior art have also been primarily limited to delivering a drug of only a single polarity at a time to a given area, at relatively low concentrations, and have not been suitable for simultaneous delivery of multiple drugs. Furthermore, there were virtually no satisfactory iontophoretic devices which were relatively simple, economical, compact, portable and capable of safe, long term delivery over several days, once applied to the patient and placed into operation. Attempts to meet these needs have involved rather complex buffering, electrical or other compensatory systems which have not proven entirely practical or satisfactory.
In addition to the foregoing difficulties, iontophoretic systems of the past have not proven effective in the administration of drugs embodying relatively large and/or heavy molecular structures. Moreover, drug formulations intended for iontophoretic therapeutic drug delivery have oftentimes required buffering agents for pH control. Control of pH at the delivery site of the therapeutic drug has been essentially unknown. Furthermore, difficulties in obtaining sufficiently high rates of infusion, due to relatively high electrical resistance and/or poor permeability at the delivery site, have also been encountered with iontophoretic systems.
The aforementioned difficulties and undesirable side effects of iontophoretic treatment have resulted in a sometimes less than enthusiastic reception of iontophoretic techniques by the medical community, in spite of the potentially great and varied advantages to be realized through their use and development.
Hence, those concerned with development and use of iontophoretic systems in the medical field have long recognized the need for a convenient and effective apparatus and method for preventing burns, irritation and the formation of vesicles and bulla on the skin in an area subjected to an iontophoretic treatment over extended periods of continuous treatment, for systems which can be physically packaged in a relatively simple, economical and compact configuration, can deliver therapeutic drugs at a relatively high rate and at higher concentrations, without the need for buffering agents and the like, which are capable of delivering large molecular substances such as insulin and the like, can deliver a plurality of drugs simultaneously in a relatively simple manner without matching drug polarity, can be used to lower resistance and increase permeability, and can be used to reliably control pH at the drug administration site. As will become apparent from the ensuing discussion, the present invention clearly fulfills all of these needs and more.
Briefly, and in general terms, the present invention provides a method and apparatus for applying electrical energy topically to a suitable surface of a biological subject, such as the skin of a human body, particularly for the long term administration of medicaments and the like or for other electrotherapeutic treatment, and by which the aforementioned deficiencies and undesired side effects are greatly minimized and may be eliminated. Moreover, the system of the present invention is relatively inexpensive to manufacture, can be physically packaged in a completely self-contained, relatively simple and compact configuration, trouble free and reliable in use, is capable of higher drug administration rates and drug concentrations, can deliver multiple drugs simultaneously in a simple manner, can control pH at the delivery site, is capable of delivering large and/or heavy molecule drugs, is a more effective bactericidal, and is arranged to be safely, simply and reliably operated for self-treatment by an average person in normal home use, even for extended periods of several days at a time. Furthermore, it is contemplated in the practice of the invention that electrical impedance at the administration site on the patient can be substantially reduced to vastly improve permeability and penetration and thereby further enhance medicament delivery.
Basically, the present invention is directed to a new and improved system for iontophoretic drug administration which includes conducting direct electrical current through the skin of a body, and periodically reversing the electrical current and conducting the current through the skin in the opposite direction, to effectively deliver very low frequency AC current, substantially in the critical range of approximately 0.0027 Hz to 10 Hz. It has been discovered that, within this substantially critical frequency window between approximately six minutes per full cycle and approximately ten cycles per second, a dramatic cancellation of skin damaging ions takes place. At frequencies higher than approximately 10 Hz, no substantial effective delivery takes place. At frequencies lower than approximately 0.0027 Hz, the risk of skin injury increases substantially.
It is well known that the positive iontophoretic electrode, in addition to its primary function of driving like polarity ionic substances into the skin of a subject, unfortunately produces skin damaging hydrochloric acid as well. Likewise, the negative iontophoretic electrode, in addition to its primary function of driving like polarity ionic substances into the skin, unfortunately also produces skin damaging sodium hydroxide. However, within the aforestated frequency range of the present invention, either driving polarity delivers the desired ionic therapeutic substances, but also cancels the undesired skin damaging ions with the reverse portion of the electrical cycle. The reason for neutralization of the harsh injury producing chemicals, i.e., hydrochloric acid and sodium hydroxide, is that both of these chemicals require a finite period of time on the skin to cause damage. Hence, these damaging chemicals are made to cancel each other before damage takes place, by critical frequency selection, in accordance with the invention, of the AC driving signal. Therefore, optimization of a long sought therapeutic device with reduced side effects has been achieved.
In accordance with the invention, electronic circuitry is provided to automatically impose the reversal of electrical current at regularly repeating intervals of time, in accordance with the aforedescribed substantially critical frequency range, and the system can be adjusted to conduct the iontophoretic treatment at any desired level of electrical current.
More specifically, the present invention is directed to a novel concept in overcoming the unwanted ions generated at the negative and positive electrodes of an iontophoretic drug delivery system, that lead to skin damage among other undesirable effects during iontophoresis. In attempting to replicate the drug delivery capability of an IV unit that would be used continuously over days, iontophoretic devices of the past are generally unsatisfactory because of their impracticality, complexity and/or the substantial skin damage they would cause. When the demand is for use over days, the new, simplified and improved technology of the present invention is required to overcome the skin damaging acid and alkali generated at the electrodes. This new technology that results in the hydrochloric acid and the sodium hydroxide canceling each other, was achieved with the aforementioned extremely low frequency alternating electrical current that mimics the drug delivery of a direct current system because it is so slow, but deposits otherwise harmful ions on the same skin area to offset or neutralize each other before skin damage can take place.
In accordance with the invention, a basic AC generator delivers a drug into the skin of a patient, but neutralizes opposing harmful chemicals that are inherently developed at the output electrodes when in an aqueous solution or gel form in contact with the skin during electrical current flow. It has been discovered that, when the electrical current is reversed at the slow rate of approximately 0.0027 Hz to 10 Hz, the behavior of the drug is to react as if it were a DC signal in that the polarity at any given moment will drive a like polarity drug component into the skin. The benefit achieved is that the unwanted chemical that was generated at the electrode was neutralized when the signal polarity reversed and developed an opposing chemical to cancel each other at the skin interface.
This non-invasive, minimal side effects system, in accordance with the invention, is designed to deliver drugs either systemically, locally or both, and is also appropriate for other iontophoretic treatment, such as sweat inhibition and the like. It can be made in two or more forms, i.e., a long lasting iontophoretic patch with self-contained electronics, or a larger unit that contains an electronics package for power and control and which terminates into output jacks. The user then plugs an electrical extension cable into these jacks and applies the other end of the cable, which terminates in a remote applicator housing suitable iontophoretic electrodes and drug reservoirs, to the patient. This larger, more powerful unit is generally intended for shorter term use. Large units, employing the frequency range of the present invention, may also be used for treating areas such as the foot which may soak in a liquid surfactant combined with an antifungal agent or the like.
Previous DC iontophoretic devices necessarily required an xe2x80x9cinactivexe2x80x9d or ground return electrode to electrically complete the circuit. Often, this electrode was remotely connected (xe2x80x9cdistalxe2x80x9d electrode) adding to an unwieldy, space devouring component. Even if the inactive electrode were adjacent to the active, drug driving electrode, it normally occupied at least fifty percent of the space of the device for its simple, one dimensional purposexe2x80x94to complete an electrical circuit. With the AC system of the present invention, the so-called xe2x80x9cinactivexe2x80x9d electrode is made active, in that it contributes to driving the drug into the skin when its alternating polarity changes to be the same polarity of the therapeutic medicament. Hence, both electrodes are used to infuse therapeutic drugs into the patient. This has another advantage from the practitioner""s view. The polarity of the drug need no longer be known in order to place it in the correct polarity drug reservoir, since the polarity of each reservoir reverses regularly. Otherwise an error could be made. The practitioner also need not stock applicators with two different capabilitiesxe2x80x94one for positive and one for negative. In effect, the applicator size is doubled because of the presence of the AC signal in accordance with the invention.
The system of the present invention also uses relatively inexpensive silicone/carbon electrodes. While this material is in common use with TENS devices (Transcutaneous Electrical Nerve Stimulators), it is not used for both electrodes for common DC iontophoretic devices. This is because these non-metallic electrodes typically show a high resistance after short use, with a consequent substantial drop in load current (especially the positive electrode). With a slow AC signal, it has been discovered that this build-up of resistance does not take place and both electrodes maintain the desired low electrical resistance. The alternative to these low cost electrodes would be pure and extremely expensive palladium, platinum or rhodium electrodes to minimize corrosion, but with the consequent possibility of metal ions being driven into the skin and further adding to xe2x80x9cclutterxe2x80x9d.
The presence of hydrochloric acid and sodium hydroxide does have a beneficial value in that these chemicals have a bactericidal effect. Each of these chemicals kill different groups of bacteria. In the conventional DC device, only one chemical is present at one electrode and, therefore, attacks only a particular group of microbes. With an AC signal, in accordance with the present invention, the antibacterial effect takes place against the groups of microbes effected by both polarities and, within the substantially critical frequency range of the invention, also avoids damage to the skin.
Heretofore, it was commonly accepted that drugs delivered by iontophoretic systems necessarily had to be limited to approximately one to two percent concentration. Increasing the concentration of the drug not only would not show an increase in drug concentration in the skin, but could actually decrease the amount of drug delivered because of xe2x80x9cclutterxe2x80x9d and competition to enter a very minute passageway (the eccrine duct). With the slow AC signal of the present invention, drug concentration can now be increased substantially beyond two percent with very important benefits that include enhanced therapeutic value and shortened treatment time.
The reason that the slow AC signal facilitates increased drug dosage or concentration above two percent is as follows: If, for instance, a positively charged drug was in the drug reservoir when the positive half of the AC signal was driving that same reservoir, then the positive component of the drug would be repelled and driven into the skin. Since all drug molecules also contain a negative component that, in this instance, would be left behind in the reservoir (in a DC device) as non-productive xe2x80x9cclutterxe2x80x9d, when the AC signal swings negative on the other half of the signal, the negative component also will be driven to the skin, thereby eliminating the aforedescribed xe2x80x9cclutterxe2x80x9d from the reservoir. This xe2x80x9ccleansingxe2x80x9d of the area, by removal of otherwise delivery inhibiting clutter, enables increased drug concentrations.
A further feature of the present invention resides in the ability to deliver drugs embodying large and/or heavy molecular structures, such as insulin, since the frequency of operation of the system of the present invention both removes xe2x80x9cclutterxe2x80x9d as a drug transfer impediment and also provides adequate molecular transport times.
In a presently preferred embodiment, the control signal generated by the system of the present invention is usually equal and opposite in all respects so that opposing unwanted chemicals cancel each other and maintain a neutral pH of approximately 7. The electrical circuitry may also be modified to favor the positive portion of the electrical cycle, rather than being exactly the same amplitude as the negative portion of the cycle. Since the skin is naturally acidic at approximately 5.6 pH, the amplitude of the positive signal would be adjusted upward to provide the pH more compatible with the skin. Of course, the opposite effect could be obtained, whenever desired, by increasing the amplitude of the negative portion of the electrical cycle relative to the positive portion.
It may be desirable to maintain a neutral pH of a drug for drug stability, permeability and irritation control among other reasons. In monopolarity DC iontophoretic devices where extremes of acid or alkaline are generated at the electrodes, the drug would quickly reach either extreme. Using an AC signal, in accordance with the invention, with substantially equal and opposite half cycles, both in amplitude and duration, would, as previously indicated, make the pH at the drug delivery site essentially neutral. However, there may be circumstances where it is desirable to controllably alter the pH from neutral. By adjusting the zero reference line, or electrical bias, of the afore-described symmetrical AC signal up or down (by switch), the positive signal can be increased or decreased in amplitude relative to the negative signal and vice versa, and, therefore, raise or lower the pH relative to neutral. Ancillary chemicals that are commonly included in drug formulations, such as buffers and isotonic drugs should be dropped from an iontophoretic drug formulation to further reduce clutter.
Furthermore, it has been discovered that there are instances where greater drug concentrations can be delivered by variations in pH from neutral and increasing the extent of the charged form of the drug to be delivered.
Modern treatment often demands the simultaneous infusion of different drugs. This is known as multi-therapy and is typically performed by inserting two catheters from two different IV units containing different medications to treat multiple problems within one patient. With a non-invasive (no catheter) iontophoretic patch, this is easily accomplished with the two reservoir system utilized by the simplified, more economical and reliable construction and method of the present invention, by placing a different drug into each reservoir. The drugs may be of the same or opposite polarity. The economy of one unit offering two distinct treatments is obvious.
In addition, since both electrodes, are xe2x80x9cactivexe2x80x9d with the arrangement of the present invention, the system can deliver twice the amount of drug compared to a comparable DC iontophoretic device. For example, if the drug to be delivered is positive and the signal in one drug reservoir were positive at any given instant, then that reservoir will deliver the drug to the skin. Simultaneously, the other reservoir will be negative and the same drug will ordinarily not flow. However, if a negative xe2x80x9ccarrier drugxe2x80x9d is made part of the formulation, then this carrier drug would flow on the negative half of the electrical cycle while pulling along the desired positively charged active drug. Thus, even though the desired drug is polarity sensitive, the system of the present invention will double the amount of drug delivered. Another embodiment utilizing the same concept is to employ an amphoteric (dipole) surfactant as part of the drug formulation. Not only does the drug flow continuously, but flow rate efficiency is very substantially enhanced because of the permeation qualities of the surfactant.
In addition to the foregoing features, the practice of the present invention may also include the preparatory process of infusing an ionic surfactant, either amphoteric or cationic, at the drug delivery site to lower load resistance by increasing permeability and penetration, and thereby enable higher levels of electrical current and drug delivery with relatively lower driving voltage. This process increases the permeability of the skin, especially the palms and soles. Electrically driving in the surfactant at the delivery site is much more effective than any presoak or swabbing.
Hence, those concerned with development and use of iontophoretic systems in the medical field have long recognized the need for a convenient and effective method and apparatus for preventing skin injury and the formation of vesicles and bulla on the skin in an area subjected to an iontophoretic treatment over extended periods of continuous treatment, which can be physically packaged in a compact and economical configuration, can deliver therapeutic drugs to deeper levels of penetration at a high rate and at higher concentrations, without the need for buffering agents, are capable of delivering large and/or heavy molecular substances, can deliver a plurality of drugs of the same or different polarity simultaneously, and can be used to control pH at the drug administration site.
These and other objects and advantages of the invention will become more readily apparent from the following more detailed description of the invention, when taken in conjunction with the accompanying drawings of illustrative embodiments.